I have 2 cheats for you!

1: this can with any character: if you're racing, hold ''R'' by a turn. if the turn is left, push your yoystick for a second to the right. do this two times, and you got a short turbo! this works also by a right turn.
2. if you play VS with 2-4 players, AND you got a long way head to the other players, stop your kart in the final lap close by the finish, spin around 180 degrees, go backward and you hear 2 finishes for you. you see then 2 points in one race!